**6. Interspecies differences in the Mixed Function Oxidase (MFO) as biomarker of exposure of different environmental contaminants**

Fibroblast cell cultures of fin whale (RT2), Bryde's whale (MBE3), sperm whale (PM6), killer whale (MOO12), Risso's dolphin (GGL1), bottlenose dolphin (TurNic), striped dolphin (RT1), long-beaked common dolphin (MDC12) and common dolphin (DDL1) were treated for 48 h with different environmental contaminants and the quantification of the induction of endogenous proteins such as CYP1A1 and CYP2B was used as target of toxicological susceptibility. The presence and the induction of CYP1A1 and CYP2B were evaluated with the indirect immunofluorescence and quantified with the Olympus macro, *DetectIntZ*. CYP1A1 is induced by planar compounds and CYP2B by globular compounds. The treatments were performed with OC mixture; flame retardants; PAHs; and BPA (Table 1). In the total mixture of Arochlor 1260 [25] only the 1.3033% shows a CYP1A1 inductive capacity while the remaining congeners are CYP2B inducers [26, 27, 28, 29, 30]. pp'DDE and pp'DDT are known as CYP2B inducers [31, 32] but an experiment on fibroblast cell culture of sperm whale (PM6) treated only with pp'DDT and pp'DDE has shown a capacity of these compounds to induce also the CYP1A1 (Figure 1). Examining at the bromine substitution patterns in the basic structure of the PBDE molecule, and with the support of the other studies on this topic [33] we can say that in the BDE-MXE mixture, the 18.72% is CYP1A1 inducer and the rest of congeners are CYP2B inducers. Benzo(a)pyrene and betanaphthoflavone are important planar compounds and CYP1A1 inducers [31]. Finally BPA that may be a human-specific inducer of the CYP3A4 gene [34], but many studies have shown that BPA inhibits several P450-dependent monooxygenases activities (CYP1A2, CYP2A2, CYP2B2, CYP2C11, CYP2D1, CYP2E1 and CYP3A2) [35].

**Figure 1.** Basal levels of immunofluorescence (AUF/nucleus) of CYP1A1 in fibroblast cells of sperm whale treated with pp'DDT and pp'DDE.
